Fore and aft seat adjusters for vehicle seats typically have a pair of parallel, floor mounted tracks that are locked to hold the seat in place, or opened to allow the seat to slide back and forth to a new position. The tracks are generally locked by a pair of rotatable lock bars, one associated with each track, which engage with a series of locking teeth under the force of a strong return spring. One lock bar, called a master lock bar, is directly operated and rotated by a manual handle, while the other, a slave lock bar, is indirectly operated in tandem with the master lock bar by a cross wire running from the master to the slave lock bar. It is important to normal adjuster operation that both lock bars remain fully closed when the handle is released, and that they both fully open when the handle is twisted.
Given a fixed cross wire length, consistent operation of the lock bars depends on holding a consistent spacing between the tracks. If the track spacing varies significantly over a manufacturing tolerance range, a dilemma is presented. If the cross wire length is tailored to the low end of the track spacing tolerance range, that is, made short enough to assure that the slave lock bar is pulled fully open when the master lock bar is opened, it may be effectively too short when the tracks are spaced farther apart. In that case, the wire may be relatively so short as to hold the slave lock bar partially open when the master lock bar is closed. A "too short" cross wire could also pull the slave lock bar open too soon, that is, before the master lock bar is fully open, thereby bottoming out and over stressing the wire. If the cross wire is instead tailored to the high end of the track spacing tolerance range, that is, made long enough to assure that the slave lock bar is fully closed when the master lock bar is closed, it may be effectively "too long" when the tracks are closer together. The slave lock bar might not fully open by the time the handle has rotated far enough to fully open the master lock bar. The seat track spacing, like any other dimension, can be carefully controlled or even redone during manufacture, so as to closely match a fixed, given cross wire length. Or, conversely, a range of various cross wire lengths could be kept on hand, and matched at assembly to each individually gauged track spacing. Either approach involves extra time, expense and, potentially, extra part inventory.